Catalysts For Ring-opening Metathesis Polymerization Research Articles

Efficient Synthesis and Cyclic Molecular Topology of Ultralarge-Sized Bicyclic and Tetracyclic Polymers

Cyclic polymers have been extensively studied because of their unique topology and physical properties, while the methods for efficient synthesis of well-defined bicyclic and multicyclic polymers are limited. Herein, an effective strategy was developed to synthesize ultralarge-sized bicyclic polymers by a ring-opening metathesis polymerization (ROMP)-based blocking-cyclization technique in a simplified feeding procedure, using the short ladderphane bearing four living ends as the initial motif. The molecular topology of the bicyclic polymer was clarified by pieces of evidence and validated by theoretical simulation. Importantly, the visualized eight-shaped molecular topology was observed. Meanwhile, the bicyclic polymer exhibited stronger thermal, fluorescence emission, and mechanical properties and better dielectric and energy storage performance than its four-arm counterpart, which elucidated the difference in molecular topology between bicyclic and four-arm polymers. Moreover, a tetracyclic polymer with a large ring size could be readily obtained. Therefore, this designed strategy opens new horizons for building bicyclic and multicyclic polymers using the conventional ROMP and commercial Grubbs catalyst.

Amine-Containing Monomers for Ring-Opening Metathesis Polymerization: Understanding Chelate Effects in Aryl- and Alkylamine-Functionalized Polyolefins

Ring-opening metathesis polymerization (ROMP) of two different types of amine-functionalized monomers, aminonorbornenes (ANs) and aminocyclooctenes (ACs), has been studied using [(H2IMes)(PCy3)(Cl)2Ru = CHPh] Grubbs second generation catalyst, G2, and [(H2IMes)(pyr)2(Cl)2Ru = CHPh] Grubbs third generation catalyst, G3. Despite the known detrimental effects of unprotected amine functionalities on Ru-based ROMP catalysts, aminopolyolefins can be readily prepared using G2 and G3. The influence of the amine substituent of the monomer on the polymerization process, as probed by monitoring reaction kinetics, confirmed that the basicity/nucleophilicity of the amine group has a detrimental influence on the ROMP process. Reaction kinetics of homopolymerization of both these classes of monomers revealed faster polymerization of ACs than the more strained AN counterpart, which has been attributed to the favored chelated catalyst resting states in the case of ANs. Hammett studies show increased polymerization rates in the presence of electron-withdrawing aryl amine-containing monomers. These observed kinetic effects were used to advantage in the copolymerization of AN and AC monomers to access a gradient polymer. Polymerization kinetics of combined monomers displayed different reactivity profiles than observed during homopolymerization. Polyolefins with unprotected secondary alkyl amines could be synthesized by leveraging the unfavorable chelate formation in the case of AC monomers. The strategic selection of cyclic alkene and relative positioning of amine substituent allows for the diverse incorporation of secondary amines into polymers by ROMP.

Monometallic and heterobimetallic ruthenium (II) and palladium (II) complexes based on a pyridine‐hydrazone ligand as bifunctional catalysts for ROMP of norbornene and ethylene polymerization

AbstractThe monometallic complex [Pd(L)(PPh3)] (mono‐Pd) was synthesized using a potentially tridentate hydrazone (H2L) and used as precursor to prepare a heterobimetallic ruthenium (II)‐palladium (II) complex [Cl2(p‐cymene)Ru(μ‐L)Pd (PPh3)] (Ru‐Pd). Mono‐Pd and Ru‐Pd were characterized by fourier transform infrared spectroscopy (FTIR), ultraviolet‐visible spectroscopy (UV–Vis), 1H, 13C{1H} and 31P{1H} nuclear magnetic ressonance(NMR) spectroscopy, elemental analysis, cyclic voltammetry, matrix‐assisted laser desorption/ionization ‐ time of flight (MALDI‐TOF) mass spectrometry, and computational methods. The mono‐Pd was additionally studied by single‐crystal X‐ray diffraction. The complex [RuCl2(p‐cymene)(Isoniazid)] (mono‐Ru) was also obtained following literature methods aiming a comparison in the catalytic activity. The ring opening metathesis polymerization (ROMP) of norbornene (NBE) using mono‐Ru or Ru‐Pd as precatalysts in the presence of ethyl diazoacetate (EDA) was evaluated as a function of time (10–60 min) using [NBE]/[EDA]/[Ru] = 5000/28/1 at 50°C. The time increases produced good yields of polyNBE, reaching 38% and 46% for mono‐Ru and Ru‐Pd, respectively. The polyNBE produced was measured by size‐exclusion chromatography (SEC) and reached an order of magnitude of 105 g·mol−1 of Mn, with Ð values ranging from 2.51 to 1.86 for mono‐Ru and from 3.50 to 1.66 for Ru‐Pd. The catalytic activity of mono‐Pd and Ru‐Pd on ethylene polymerization was assessed with a range of [Al]/[Pd] molar ratio between 350 and 1750, 30–70°C temperature, 2 to 4 h reaction time, and total reaction volume of 25 and 50 ml. Mono‐Pd achieved an activity of 22.80 kg PE (mol Pd)−1 h−1 at 60°C after 4 h using [Al]/[Pd] = 1050, 7 μmol of catalyst in 25 ml of toluene, and 116 psi ethylene. For Ru‐Pd, an activity of 20.35 kg PE (mol Pd)−1 h−1 at 60°C after 4 h was obtained using [Al]/[Pd] = 1750, 7 μmol of catalyst in 25 ml of toluene, and 116 psi ethylene. Overall, Ru‐Pd showed to be active in both ROMP and ethylene polymerization reactions, being categorized as a bifunctional catalyst.

Synthesis and characterization of a novel latent ring-opening metathesis polymerization catalyst

The synthesis and characterization of a novel latent ruthenium catalyst bearing a chelate ligand containing an oxadiazole fragment for the olefin metathesis are described. The main advantages of the utilization of this ligand are the straightforwardness of preparation, mild reaction conditions, and availability of the feedstock. Preliminary study of the catalytic activity of the Ru complex for metathesis reactions demonstrated its inactive nature for the ring-closing metathesis (RCM), but an excellent thermo-switchability for the ring-opening metathesis polymerization of norbornene.

Survey of Catalysts for Frontal Ring-Opening Metathesis Polymerization

Survey of Catalysts for Frontal Ring-Opening Metathesis Polymerization

Preparation and activity of ruthenium catalyst based on β-cyclodextrin for ring-opening metathesis polymerization

Inspired by substrates-recognition of enzymes, we prepared supramolecular catalyst (Ru-βCD Cat) for ring-opening metathesis polymerization (ROMP) by modifying second generation Grubbs catalyst® (M204) with β-cyclodextrin (βCD) derivative (VPhe-βCD). The ROMP activity of Ru-βCD Cat was demonstrated using 7-oxanorbornene-2,3-dicarboxylic acid dimethyl ester (ONorCOOMe). The VPhe-βCD cavity recognized the ONorCOOMe monomer and attached to catalytic metal center of Ru-βCD Cat to grow poly(ONorCOOMe) with higher yield and molecular weight (Mn) in aqueous medium. The yield and Mn were higher than those of poly(ONorCOOMe) obtained by second generation Hoveyda-Grubbs catalyst® (M720). 1-Adamantanol hindered ONorCOOMe from occupying the βCD cavity, acting as a competitive guest molecule. The inhibition caused lower polymer yield and Mn. These results showed that molecular recognition of ONorCOOMe by the cavity of Ru-βCD Cat is important to increase the polymer yield and Mn of poly(ONorCOOMe).

It is Better with Salt: Aqueous Ring-Opening Metathesis Polymerization at Neutral pH.

Aqueous ring-opening metathesis polymerization (ROMP) is a powerful tool for polymer synthesis under environmentally friendly conditions, functionalization of biomacromolecules, and preparation of polymeric nanoparticles via ROMP-induced self-assembly (ROMPISA). Although new water-soluble Ru-based metathesis catalysts have been developed and evaluated for their efficiency in mediating cross metathesis (CM) and ring-closing metathesis (RCM) reactions, little is known with regards to their catalytic activity and stability during aqueous ROMP. Here, we investigate the influence of solution pH, the presence of salt additives, and catalyst loading on ROMP monomer conversion and catalyst lifetime. We find that ROMP in aqueous media is particularly sensitive to chloride ion concentration and propose that this sensitivity originates from chloride ligand displacement by hydroxide or H2O at the Ru center, which reversibly generates an unstable and metathesis inactive complex. The formation of this Ru-(OH)n complex not only reduces monomer conversion and catalyst lifetime but also influences polymer microstructure. However, we find that the addition of chloride salts dramatically improves ROMP conversion and control. By carrying out aqueous ROMP in the presence of various chloride sources such as NaCl, KCl, or tetrabutylammonium chloride, we show that diblock copolymers can be readily synthesized via ROMPISA in solutions with high concentrations of neutral H2O (i.e., 90 v/v%) and relatively low concentrations of catalyst (i.e., 1 mol %). The capability to conduct aqueous ROMP at neutral pH is anticipated to enable new research avenues, particularly for applications in biological media, where the unique characteristics of ROMP provide distinct advantages over other polymerization strategies.

Organic and Organometallic Chemistry at the Single-Molecule, -Particle, and -Molecular-Catalyst-Turnover Level by Fluorescence Microscopy.

Mechanistic studies have historically played a key role in the discovery and optimization of reactions in organic and organometallic chemistry. However, even apparently simple organic and organometallic transformations may have surprisingly complicated multistep mechanisms, increasing the difficulty of extracting this mechanistic information. The resulting reaction intermediates often constitute a small fraction of the total reaction mixture, for example, creating a long-term analytical challenge of detection. This challenge is particularly pronounced in cases where the positions of intermediates on the reaction energy surface mean that they do not "build up" to the quantities needed for observation by traditional ensemble analytical tools. Thus, their existence and single-step elementary reactivity cannot be studied directly. New approaches for obtaining this otherwise-missing mechanistic information are therefore needed. Single-turnover, single-molecule, single-particle, and other subensemble fluorescence microscopy techniques are ideally suited for this role because of their sensitivity and spatiotemporal resolution. Inspired by the robust development of single-molecule fluorescence microscopy tools for studying enzyme catalysis, our laboratory has developed analogous fluorescence microscopy techniques to overcome mechanistic challenges in synthetic chemistry, with sensitivity as high as the single-complex, single-turnover, and single-molecule level. These techniques free the experimenter from the previous restriction that intermediates must "build up" to quantities needed for detection by ensemble analytical tools and are suited to systems where synchronization through flash photolysis or stopped flow would be inconvenient or inaccessible. In this process, the techniques transform certain previously "unobservable" intermediates and their elementary single-step reactivities into "observable" ones through sensitive and selective spectral handles. Our program has focused on imaging reactions in small-molecule, organic, and polymer synthetic chemistry with an accent on the reactivity of molecular transition metal complexes and catalysts. Our laboratory initiated studies in this area in 2008 with the imaging of individual palladium complexes that were tagged with spectator fluorophores. To enable imaging, we started with fluorophore selection and development, overcame challenges with imaging in organic solvents, and developed strategies compatible with air-sensitive chemistry and concentrations of reagents generally used in small-molecule synthesis. These studies grew to include characterization of previously unknown organometallic intermediates in the synthesis of organozinc reagents and the direct study of their elementary-step reactivity. The ability to directly observe this behavior generated predictive power for selecting salts that accelerated organozinc reagent formation in synthesis, including salts that had not yet been reported synthetically. In 2017 we also developed the first single-turnover imaging of molecular (chemo)catalysts, which through the technique's spatiotemporal resolution revealed abruptly time-variable polymerization kinetics wherein molecular ruthenium ring-opening metathesis polymerization (ROMP) catalysts changed rates independently from other catalysts less than 1 μm away. Individual catalytic turnovers, each corresponding to one single-chain-elongation reaction arising from insertion of single ROMP or enyne monomers at individual Grubbs II molecular ruthenium catalysts, were spatiotemporally resolved as green flashes in growing polymers. In this Account, we discuss the development of this technique from idea to application, including challenges overcome and strategies created to image synthetic organic and organometallic molecular chemistry at the highest levels of detection sensitivity. We also describe challenges not yet solved and provide an outlook for this growing field at the intersection of microscopy and synthetic/molecular chemistry.

(Arylimido)vanadium(V)-Alkylidene Complexes as Catalysts for Ring-opening Metathesis Polymerization (ROMP) of Cyclic Olefins: Ligand Design for Exhibiting the High Activity

(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(OR′)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3; R′ = 2,6-Me2C6H3, 2,6-iPr2C6H3, 2,6-F2CeH3, C6F5, C6Cl5] exhibited from moderate to remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene (NBE). The catalytic activities were affected by the ligand substituents, and V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6X5)(PMe3)2 (X = F, Cl) demonstrated the exceptionally high catalytic activities for ROMP of NBE. The complexes polymerized cycloheptene (CHPE) and cis-cyclooctene (COE), and ROMP of COE by the OC6Cl5 analogue proceeded in a living manner even at 80 °C, and the activity increased with increasing the temperature up to 120 °C. Highly active catalysts for ROMP of cyclic olefins (NBE, cyclopentene, and CHPE) can be generated in situ by premixing isolated V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 with 1.0 equiv. of C6F5OH or C6Cl5OH via immediate phenoxy exchange; the activity was affected by the kind of phenol added [TOF in the ROMPs of NBE: 4.62 × 104 min−1 (upon addition of C6F5OH) versus 37.3 min−1 (none)].

Anchor Peptide-Mediated Surface Immobilization of a Grubbs-Hoveyda-Type Catalyst for Ring-Opening Metathesis Polymerization.

Adhesion promoting peptides have been reported to enable efficient enzyme immobilization on various material surfaces. Here we report the first immobilization of a synthetic Grubbs-Hoveyda (GH) type catalyst on two different materials (silica and polypropylene). To this end, the GH catalyst was coupled to an engineered (F16C) variant of the adhesion promoting peptide LCI through thiol-maleimide "click" reaction. Immobilization was performed in an oriented manner through the adhesion promoting peptide by simple incubation with the materials in water and subsequent washing with water and tetrahydrofuran. The immobilized GH catalyst was probed in ring-opening metathesis polymerization of a norbornene derivative to alter the surface properties in a layer-by-layer fashion.

Recent development in polyolefin-based anion exchange membrane for fuel cell application

Anion exchange membrane (AEM) plays a critical role in many environmental and energy devices and processes, such as fuel cell, redox flow battery, and electrodialysis. In particular, when polymeric AEMs are exploited in alkaline fuel cells to replace liquid electrolytes, AEM fuel cells (AEMFC) have attracted worldwide attention because of several inherent advantages over proton exchange membrane fuel cells, e.g. the utilization of less expensive metallic catalysts and enhanced kinetics of oxygen reduction. Among different kinds of AEMs, polyolefin-based AEMs showed great potential for large-scale commercialization because of their excellent chemical stability, easy processability, and low cost. The strategies to synthesize polyolefin anion exchange membrane materials included direct (co)polymerization with functionalized monomers and post-modification of polyolefins. Generally, the ring-opening metathesis polymerization and Ziegler-Natta catalyst mediated polymerization techniques have been successfully employed to synthesized polyolefin AEMs, using the functional monomers including the α-olefin, norbornene, and cyclooctene. Therefore, the chemical structure and composition can be readily tuned to achieve the optimized properties of the resulting AEMs. However, the functional monomers that need complex synthetic procedure have greatly hampered its further commercialization. Radiation-grafting polymerization of vinylbenzyl chloride (VBC) on the polyolefin backbone has been confirmed as another effective method to produce AEMs. Both (partially or fully) fluorinated and hydrocarbon-based polyolefin have been grafted with poly(VBC) under high energy radiation (such as commercial electron-beam accelerators or 60Co γ-ray facilities), and subsequent quaternization allow the synthesis of AEMs with different ionic head-group. In order to produce high-performance AEMs, high irradiation doses were used to get high degree of grafting, which in turn results in a detrimental reduction in the mechanical properties of the resulting AEMs. Therefore, it is necessary to optimise the conditions of grafting reactions. The physicochemical properties of polyolefin-based AEMs are investigated in detail by the measurement of ion exchange capacity, water uptake, swelling ratio, and ionic conductivity, which are well corelated to their chemical structure and microstructure. Moreover, H2/O2 AEMFC assembled from polyolefin-based AEMs (especially for radiation-grafted AEMs) are tested under various conditions in terms of types of electrochemical catalysts, cell temperature, gas flow rate, and so on. Thus, this review summarized the recent developments of polyolefin-based AEMs from the synthetic methods to the properties of AEMs and their performance in H2/O2 fuel cell. The relationship between chemical structure, properties and morphology of polyolefin-based AEMs will be discussed. At last, we extend the discussion of AEMs to their performance in H2/O2 fuel cell, as dramatic improvements of AEM fuel cell performance is accomplished when using high- performance polyolefin-based AEMs.

Ring‐Opening Metathesis Polymerization in Aqueous Media Using a Macroinitiator Approach

AbstractWater‐soluble and amphiphilic polymers are of great interest to industry and academia, as they can be used in applications such as biomaterials and drug delivery. Whilst ring‐opening metathesis polymerization (ROMP) is a fast and functional group tolerant methodology for the synthesis of a wide range of polymers, its full potential for the synthesis of water‐soluble polymers has yet to be realized. To address this, we report a general strategy for the synthesis of block copolymers in aqueous milieu using a commercially available ROMP catalyst and a macroinitiator approach. This allows for excellent control in the preparation of block copolymers in water. If the second monomer is chosen such that it forms a water‐insoluble polymer, polymerization‐induced self‐assembly (PISA) occurs and a variety of self‐assembled nano‐object morphologies can be accessed.

Ring-Opening Metathesis Polymerization in Aqueous Media Using a Macroinitiator Approach.

Water-soluble and amphiphilic polymers are of great interest to industry and academia, as they can be used in applications such as biomaterials and drug delivery. Whilst ring-opening metathesis polymerization (ROMP) is a fast and functional group tolerant methodology for the synthesis of a wide range of polymers, its full potential for the synthesis of water-soluble polymers has yet to be realized. To address this, we report a general strategy for the synthesis of block copolymers in aqueous milieu using a commercially available ROMP catalyst and a macroinitiator approach. This allows for excellent control in the preparation of block copolymers in water. If the second monomer is chosen such that it forms a water-insoluble polymer, polymerization-induced self-assembly (PISA) occurs and a variety of self-assembled nano-object morphologies can be accessed.

Accessible ring opening metathesis and atom transfer radical polymerization catalysts based on dimethyl sulfoxide ruthenium(II) complexes bearing N-heterocyclic carbene ligands

Dimethyl sulfoxide ruthenium(II) complexes of N-heterocyclic carbenes derived from cycloalkylamines (cycloalkyl = cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl (1d)) were synthesized: [RuCl2(S-dmso)2(IPent)] (2a), [RuCl2(S-dmso)2(IHex)] (2b), [RuCl2(S-dmso)2(IHept)] (2c), and [RuCl2(S-dmso)2(IOct)] (2d). The imidazolium salts 1a-1d were characterized by FTIR, UV–vis, and 1H and 13C NMR spectroscopy, while their respective dimethyl sulfoxide ruthenium(II) complexes (2a-2d) were characterized by elemental analysis, FTIR, UV–vis, 1H and 13C NMR, and cyclic voltammetry. The complexes 2a-2d were evaluated as catalytic precursors for ROMP of norbornene (NBE) and for ATRP of methyl methacrylate (MMA). The polynorbornene (polyNBE) syntheses via ROMP using the complexes 2a-2d as pre-catalysts were evaluated under reaction conditions of [EDA]/[Ru] = 28 (5 μL), [NBE]/[Ru] = 5000 at 50 °C as a function of time. The polymerization of MMA via ATRP was conducted using the complexes 2a-2d in the presence of ethyl 2-bromoisobutyrate (EBiB) as the initiator. All tests were using the molar ratio [MMA]/[EBiB]/[Ru] = 1000/2/1 and conducted at 85 °C. The linear correlation of ln([MMA]0/[MMA]) and time clearly indicates that the concentration of radicals remains constant during the polymerization and that the ATRP of MMA mediated by 2a-2d proceeds in a controlled manner.

In Situ Generated Ruthenium-Arene Catalyst for Photoactivated Ring-Opening Metathesis Polymerization through Photolatent N-Heterocyclic Carbene Ligand.

1,3-Bis(mesityl)imidazolium tetraphenylborate (IMesH+ BPh4- ) can be synthesized in one step by anion metathesis between the corresponding imidazolium chloride and sodium tetraphenylborate. In the presence of 2-isopropylthioxanthone (sensitizer), an IMes N-heterocyclic carbene (NHC) ligand can be photogenerated under irradiation at 365 nm through coupled electron/proton transfer reactions. By combining this tandem NHC photogenerator system with metathesis inactive [RuCl2 (p-cymene)]2 precatalyst, the highly active RuCl2 (p-cymene)(IMes) complex can be formed in situ, enabling a complete ring-opening metathesis polymerization (ROMP) of norbornene in the matter of minutes at room temperature. To the best of our knowledge, this is the first example of a photogenerated NHC. Its exploitation in photoROMP has resulted in a simplified process compared to current photocatalysts, because only stable commercial or easily synthesized reagents are required.

Single Turnover at Molecular Polymerization Catalysts Reveals Spatiotemporally Resolved Reactions.

Multiple active individual molecular ruthenium catalysts have been pinpointed within growing polynorbornene, thereby revealing information on the reaction dynamics and location that is unavailable through traditional ensemble experiments. This is the first single-turnover imaging of a molecular catalyst by fluorescence microscopy and allows detection of individual monomer reactions at an industrially important molecular ruthenium ring-opening metathesis polymerization (ROMP) catalyst under synthetically relevant conditions (e.g. unmodified industrial catalyst, ambient pressure, condensed phase, ca. 0.03 m monomer). These results further establish the key fundamentals of this imaging technique for characterizing the reactivity and location of active molecular catalysts even when they are the minor components.

A Ring-Opening Metathesis Polymerization Catalyst That Exhibits Redox-Switchable Monomer Selectivities.

A ring-opening metathesis polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of polymerization reactions.

Protection of graphene supported ROMP catalyst through polymeric globular shell in self-healing materials

Abstract Protected Ru-catalyst, immobilized on graphene sheets, was prepared and used for Ring Opening Metathesis Polymerization (ROMP) in strongly reactive environments based on epoxy resins. The protection mechanism, proposed in this paper, is based on the formation of a micrometric globular shell that partially englobed the catalytic site, causing hindrances for the deactivation of the catalyst due to an equimolecular reaction between the catalyst complex and the oxirane ring. The catalytic performance evaluated in reactive self-healing systems showed the overcoming of several critical drawbacks. The proposed system allows curing temperatures typical of structural materials and, in addition to preventing the agglomeration of the catalyst particles, a remarkable reduction from 5% to 0.3% by wt of expensive catalyst in the self-healing composite material.

Designing Sequence Selectivity into a Ring-Opening Metathesis Polymerization Catalyst.

The development of a chemoselective catalyst for the sequence-selective copolymerization of two cycloolefins by ring-opening metathesis polymerization is described, starting with the mechanistic work that established the structure of the key metallacyclobutane intermediate. Experimental and computational investigations converged to a conclusion that the lowest energy metallacyclobutane intermediate in the ruthenium carbene-catalyzed metathesis reaction had the four-membered ring trans to the phosphine or NHC ligand. The trans-metallacyclobutane structure, for the case of a degenerate metathesis reaction catalyzed by a Grubbs first-generation complex, necessitated a rotation of the 3-fold symmetric tricyclohexylphosphine ligand, with respect to the 2-fold symmetric metallacyclobutane substructure. The degeneracy could be lifted by constraining the rotation. Lifting the degeneracy created the possibility of chemoselectivity. This mechanistic work led to a concept for the "tick-tock" catalyst for a chemoselective, alternating copolymerization of cyclooctene and norbornene from a mixture of the two monomers. The design concept could be post facto elaborated in terms of stereochemistry and topological theory, both viewpoints providing deeper insight into the design of selectivity into the catalytic reaction. The iterative interaction of theory and experiment provided the basis for the rational design and optimization of a new selectivity into an existing catalytic system with decidedly modest structural modifications of the original carbene complex.

ChemInform Abstract: Developments in Externally Regulated Ring‐Opening Metathesis Polymerization

AbstractReview: [32 refs.